COMET • Vol. 12, No. 13 – 28 June 2011

COMET is now on its annual summer hiatus and will resume publication in August when the 2011-2012 academic year commences. COMET’s home page contains a “search” feature that you may find helpful in researching various mathematics education topics in the COMET archives (2000-2011): http://comet.cmpso.org

This is a good time for some general “housekeeping.” Please let me know if you would like COMET sent to a different email account or if you are receiving multiple issues at the same address.

If you are conducting a professional development institute or teaching a course for prospective teachers and would like to offer COMET subscriptions to your participants/students, I would be happy to add those who are interested to the COMET distribution list. Simply email me a MS Word or Excel document containing their email addresses.

I leave you tonight with sincere wishes for an enjoyable summer plus links to a few “interesting” articles about Tau Day, which some mathematicians were apparently celebrating today. :- )

We all know about Pi Day, that tasty holiday on March 14 where celebrations include reciting digits of Pi and eating pie. At MIT, we ate pizza pie, pine nuts, and dined on dozens of types of sugary and fruity pies. Today, on what’s usually called “2 Pi Day”‘ (do you bake twice as many pies as you usually would?) we’re seeing headlines about “pi being under attack”‘ and the movement to replace pi with another constant… tau?

Why tau instead of pi? We all know that pi is the circumference (C) of a circle divided by its diameter (D): pi = C/D = 3.14159…

Pi (p) is used constantly (no pun intended) in math, and shows up everywhere in nature. It’s irrational, meaning you can’t get it from a fraction of whole numbers, and it’s also transcendental, meaning that it’s not the root of a non-constant polynomial equation [with rational coefficients]. Pi, however, isn’t the most fundamental constant that could be used in geometric and mathematical expressions: it’s actually “a confusing and unnatural choice”‘ to be used as a circle constant, according to Dr. Michael Hartl of TauDay.com and author of the Tau Manifesto.

A more fundamental ratio for the circle constant is that of a circle’s circumference (C) to its radius (r): circle constant = C/r = 6.283185…

This number is numerically equal to 2p (since the diameter is equal to 2r), and is called tau, or t; and like p, is also irrational and transcendental. Tau makes much more sense in mathematical formulas, especially in trigonometry: its value relates the full turn of a circle, not just half as with p, to a constant. Tau describes 360 degrees, not just 180 degrees. In this context, t is the more natural choice to use not just when talking about angles on a circle, but in general mathematics and beyond.